Flexural resonator element and flexural resonator for reducing energy loss due to heat dissipation

ABSTRACT

A flexural resonator element includes a base body and a beam with a groove and a through-hole, the beam being extended in a Y direction from the base body and flexurally vibrating in an X direction orthogonal to the Y direction, the groove being formed on a surfaces of the beam perpendicular to a Z direction orthogonal to the X direction and the Y direction, and the through-hole having a smaller width in the X direction than a width of an opening of the groove in the X direction and penetrating from an inner surface of the groove formed on the surface of the beam to a surface of the beam opposite to the surface of the beam having the groove.

This is a Continuation of application Ser. No. 12/706,728 filed Feb. 17,2010. The disclosure of the prior application is hereby incorporated byreference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a flexural resonator element and aflexural resonator.

2. Related Art

In general, a flexural resonator element includes a vibrating beam.Flexural vibration of the beam causes oscillation to drive the flexuralresonator element. When the flexural resonator element is driven,flexural deformation of the beam repeatedly occurs. At a certain moment,when the beam is flexurally deformed, compression displacement is causedin a region near a first side surface of the beam in a deformingdirection, and expansion displacement is caused in a region near asecond side surface of the beam opposite to the first side surfacethereof. Thereby, at the moment, temperature in the compressed region ofthe beam increases, whereas temperature in the expanded region of thebeam decreases. Then, at a next moment, the beam is deformed in adirection opposite to the above deforming direction, whereby thecompressed region and the expanded region are switched each other.

When focusing attention on the compressed or expanded region, a cycle ofincrease and decrease in temperature is repeated in the region byvibration of the beam. Accordingly, when heat input or output occursbetween the compressed or expanded region and another region, vibrationenergy of the beam is dissipated as heat energy, reducing vibrationenergy efficiency in the flexural resonator element. Such an energy lossis more noticeable in more compact flexural resonator elements and seemsto be one of reasons why miniaturization of flexural resonator elementsresults in a small Q value.

To solve the problem, for example, JP-UM-A-2-032229 discloses aresonator including a hole and a groove. The hole has a same openingarea both on upper and lower surfaces of a beam to allow a compressed orexpanded region to be structurally independent from an other region. Thegroove is provided to delay the input or output of heat between thecompressed or expanded region and the other region.

Miniaturization of flexural resonator elements has increasingly beendemanded. To meet the demand, there is used a beam having an extremelysmall width. This makes it very difficult to form a groove as in theconventional art on the beam in order to increase the efficiency in theresonator element. In other words, although there is a need forformation of a narrow groove with a large depth, it is more difficult toform a narrower groove by an ordinary etching process. Additionally,mechanical strength of the beam is reduced by formation of thepenetrating through-hole having the same opening area both on the upperand the lower surfaces of the beam.

Furthermore, a wiring electrode formed on the beam having a small widthneeds to also have a small size. This tends to cause wiring electrodebreaking or unnecessary short circuit.

SUMMARY

An advantage of the present invention is to provide a flexural resonatorelement that can reduce energy loss and can be easily produced althoughcompact in size, thus ensuring high reliability. Another advantage ofthe invention is to provide a flexural resonator including the flexuralresonator element.

A flexural resonator element according to a first aspect of theinvention includes a base body and a beam with a groove and athrough-hole, the beam being extended in a Y direction from the basebody and flexurally vibrating in an X direction orthogonal to the Ydirection, the groove being formed on a surface of the beamperpendicular to a Z direction orthogonal to the X direction and the Ydirection, and the through-hole having a smaller width in the Xdirection than a width of an opening of the groove in the X directionand penetrating from an inner surface of the groove formed on thesurface of the beam to a surface of the beam opposite to the surface ofthe beam having the groove.

In the flexural resonator element above, energy loss is reduced, and theflexural resonator element having a compact size can be easily produced.In addition, the flexural resonator element produced is highly reliable.

Preferably, in the flexural resonator element, the through-hole includesa plurality of through-holes, the plurality of through-holes beingformed in the groove.

Preferably, in the flexural resonator element, the groove formed on theat least one surface of the beam includes two grooves.

Preferably, in the flexural resonator element, the two grooves areformed on one of two surfaces of the beam perpendicular to the Zdirection.

Preferably, in the flexural resonator element, each of the two groovesis formed on a different one of two surfaces of the beam perpendicularto the Z direction.

Preferably, in the flexural resonator element, the through-holepenetrates from the inner surface of the groove formed on one of the twosurfaces of the beam to the inner surface of the groove formed on another one of the two surfaces of the beam.

Preferably, in the flexural resonator element, the beam includes a firstelectrode provided on the inner surface of the groove, a secondelectrode provided on a surface of the beam perpendicular to the Xdirection, and a plug provided on an inner surface of the through-hole.

Preferably, in the flexural resonator element, the base body and thebeam are made of quartz crystal.

Preferably, the flexural resonator element is of a tuning fork type inwhich the beam includes two cantilevered beams extended in parallel toeach other from the base body.

Preferably, in the flexural resonator element, the base body includes abase portion and a pair of connecting portions extended from the baseportion in directions opposite to each other, and the beam includes apair of detection beams extended from the base portion in directionsopposite to each other and two pairs of driving beams extended from theconnecting portion in directions opposite to each other.

Preferably, the flexural resonator element is of a double-ended tuningfork type in which the base body includes two base bodies, the beamincludes two beams formed in parallel to each other, opposite ends ofeach of the two beams being supported by the two base bodies, and thegroove formed on the each beam includes four grooves, each two of thefour grooves being formed on a different one of the two surfaces of thebeam perpendicular to the Z direction.

Preferably, in the flexural resonator element of the double-ended tuningfork type, the base bodies form a frame-shaped portion having an openingportion formed within the frame-shaped portion, and the two beams areformed in parallel to each other in the opening portion, the oppositeends of each of the beams being supported by the frame-shaped portion ofthe base bodies.

Preferably, in the flexural resonator element, the each two groovesformed on the different one of the two surfaces of the beam are orientedin mutually opposite directions, and the through-hole penetrates fromthe inner surface of each of the grooves formed on one of the twosurfaces to the inner surface of each of the grooves formed on an otherone of the surfaces.

A flexural resonator according to a second aspect of the inventionincludes the flexural resonator element of the first aspect, a casinghousing the flexural resonator element, and a cover sealing the casing.

In the flexural resonator of the second aspect, energy loss is reduced,and the flexural resonator having a compact size can be easily produced.In addition, the flexural resonator produced is highly reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a plan view schematically showing a flexural resonator element100 according to a first embodiment of the invention.

FIGS. 2A and 2B are sectional views schematically showing an example ofa shape of a beam in the flexural resonator element 100 of the firstembodiment.

FIGS. 3A and 3B are sectional views schematically showing a modifiedexample of the shape of the beam in the flexural resonator element 100of the first embodiment.

FIGS. 4 A and 4B are sectional views schematically showing anothermodified example of the shape of the beam in the flexural resonatorelement 100 of the first embodiment.

FIG. 5 is a plan view schematically showing a flexural resonator element200 according to a second embodiment of the invention.

FIGS. 6A and 6B are sectional views schematically showing an example ofa shape of a beam in the flexural resonator element 200 of the secondembodiment.

FIGS. 7A and 7B are sectional views schematically showing a modifiedexample of the shape of the beam in the flexural resonator element 200of the second embodiment.

FIG. 8 is a plan view schematically showing a flexural resonator element300 according to a third embodiment of the invention.

FIGS. 9A and 9B are sectional views schematically showing an example ofa shape of a beam in the flexural resonator element 300 of the thirdembodiment.

FIGS. 10A and 10B are sectional views schematically showing a modifiedexample of the shape of the beam in the flexural resonator element 300of the third embodiment.

FIG. 11 is a plan view schematically showing a flexural resonatorelement 400 according to a fourth embodiment of the invention.

FIGS. 12A and 12B are sectional views schematically showing an exampleof a shape of a beam in the flexural resonator element 400 of the fourthembodiment.

FIGS. 13A and 13B are sectional views schematically showing a modifiedexample of the shape of the beam in the flexural resonator element 400of the fourth embodiment.

FIGS. 14A and 14B are sectional views schematically showing anothermodified example of the shape of the beam in the flexural resonatorelement 400 of the fourth embodiment.

FIG. 15 is a schematic diagram illustrating an electric field applied tothe beam of the flexural resonator element 400.

FIG. 16 is a plan view schematically showing a flexural resonatorelement 500 according to a fifth embodiment of the invention.

FIG. 17 is a plan view schematically showing a flexural resonatorelement 600 according to a sixth embodiment of the invention.

FIG. 18 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 19 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 20 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 21 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 22 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 23 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 24 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 25 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 26 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 27 is a sectional view schematically showing a step for producingthe flexural resonator element according to the embodiments of theinvention.

FIG. 28 is a sectional view schematically showing a flexural resonator1000 according to an embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention will be described with reference to theaccompanying drawings. It should be noted that the embodiments describedbelow are merely examples of the invention.

1. Flexural Resonator Element

For example, a flexural resonator element according to the embodimentsof the invention may be of a single beam type, a tuning fork type, adouble-ended tuning fork type, or a combination type thereof (such as aso-called double T-shaped resonator element). Among them, exemplaryembodiments of a tuning fork flexural resonator element, a double-endedtuning fork flexural resonator element, and a double T-shaped flexuralresonator element will be sequentially described hereinafter.

1-1. Tuning Fork Flexural Resonator Element

FIGS. 1 to 14 are schematic views showing examples of the flexuralresonator element according to respective embodiments of the invention.The drawings show respective examples of a tuning fork flexuralresonator element. FIG. 1 is a plan view schematically showing aflexural resonator element 100 according to a first embodiment of theinvention. FIGS. 2A, 2B to FIGS. 4A, 4B are sectional viewsschematically showing examples of a shape of a beam included in theflexural resonator element 100. FIG. 5 is a plan view schematicallyshowing a flexural resonator element 200 according to a secondembodiment of the invention. FIGS. 6A, 6B and FIGS. 7A, 7B are sectionalviews schematically showing examples of a shape of a beam included inthe flexural resonator element 200. FIG. 8 is a plan view schematicallyshowing a flexural resonator element 300 according to a third embodimentof the invention. FIGS. 9A, 9B and FIGS. 10A, 10B are sectional viewsschematically showing examples of a shape of a beam included in theflexural resonator element 300. FIG. 11 is a plan view schematicallyshowing a flexural resonator element 400 according to a fourthembodiment of the invention. FIGS. 12A, 12B to FIGS. 14A, 14B aresectional views schematically showing examples of a shape of a beamincluded in the flexural resonator element 400. Each of the sectionalviews corresponds to a section taken along line A-A drawn in an eachcorresponding plan view. In each plan view and in each left-sidesectional view of the beam, there is not shown any electrode. FIG. 15 isa schematic diagram illustrating an electric field applied to a beam 20included in the flexural resonator elements above.

The flexural resonator element according to the embodiments of theinvention includes a base body 10 and the beam 20. The flexuralresonator elements 100 to 400 exemplified in the respective drawingsinclude two beams 20. The two beams 20 vibrate in directions comingclose to and apart from each other.

The base body 10 may serve as a base portion of each of the flexuralresonator elements 100 to 400. Specifically, the base body 10 may beused as a portion where any one of the flexural resonator elements 100to 400 is fixed to a package or a portion where there is formed a padfor outwardly leading the electrode formed on each of the beams 20. Thebase body 10 may be formed integrally with the beams 20. The base body10 has an arbitrary shape. For example, the base body 10 may have anapproximately rectangular parallelepiped shape as shown in the drawingsor a frame shape surrounding peripheries of the beams 20 so as tosupport the beams 20 within the frame. In addition, the base body 10 mayhave a substrate-like shape having a thickness in a Z direction andexpanded in a direction parallel to an XY plane orthogonal to the Zdirection (the Z direction and the XY plane may be the same as thosedefined in a description of the beams 20 that will be described later).The thickness of the base body 10 may be the same as or different fromthat of the beams 20. The base body 10 may have piezoelectricproperties. A material of the base body 10 can be arbitrarily selected.The base body 10 formed integrally with the beams 20 described later maybe made of a same material as that of the beams 20, for example, apiezoelectric material such as quartz crystal, lithium tantalite, orlithium niobate.

Each of the beams 20 is extended from the base body 10. In the presentspecification, an extending direction of the each beam 20 is referred toas a Y direction. The beam 20 is extended in the Y direction from thebase body 10 and flexurally vibrates in an X direction orthogonal to theY direction. Accordingly, it can be said that the beams 20 flexurallyvibrate in the XY plane. Additionally, in the specification, a directionorthogonal to the X direction and the Y direction is referred to as theZ direction. The beams 20 can serve as a vibrating portion in theflexural resonator elements 100 to 400. The each beam 20 has a columnarshape. For example, a section of the beam 20 taken along a ZX plane mayhave a polygonal or quadrangular shape. In the examples shown in thedrawings, an outline (envelope) of the section of the beam 20 takenalong the ZX plane has an approximately square shape. Preferably, thebeam 20 has a quadrangular prism shape because of easy production. Thebeams 20 are made of a piezoelectric material that allows flexuralvibration upon application of a voltage signal. The material of thebeams 20 may be quartz crystal, lithium tantalite, lithium niobate, orthe like. The beams 20 made of any of the materials are formed so as toflexurally vibrate in the X direction by appropriately selecting acrystal azimuth of the material, locations of the electrodes formed onthe beams 20, a driving method, and the like. When the beams 20 are madeof quartz crystal, the beams 20 can be formed, for example, bypatterning of a substrate called as a Z plate whose normal direction ispositioned near a Z axis of the quartz crystal.

Each of the beams 20 includes a groove 22 and a through-hole 24.

The groove 22 is formed on at least one of two surfaces of the beam 20perpendicular to the Z direction and is a recessed portion having abottom and a depth in the Z direction. The groove 22 has an arbitraryshape. Preferably, the depth of the groove 22 is in a range of 10 to 90%of a thickness of the beam 20 in the Z direction. In addition, the depthof the groove 22 may have a distribution in the groove 22. In theexample of FIG. 1, a planar shape of the groove 22 is a long and narrowrectangular shape extended in a lengthwise direction of the beam 20.However, instead of that, the groove 22 may have a round, oblong, oroval planar shape, for example. In the groove 22 with the long andnarrow planar shape, heat conduction between portions of the beam 20positioned on opposite sides of the groove 22 can be more efficientlysuppressed. For example, a planar size of the groove 22 may be in arange of 10 to 80% of a length of the beam 20. Preferably, the groove 22is formed so as to be closer to a portion of the beam 20 connecting withthe base body 10. This allows the groove 22 to be positioned in a regionexhibiting a large amount of deformation when the beam 20 is bent, sothat a mass can be left near a top end of the beam 20. Furthermore, inassociation with leading of the electrode or the like, and whenperforming frequency adjustments of the flexural resonator elements 100to 400 by adhering a weight material to the top end of each beam 20, itis unnecessary to form the groove 22 over an entire length of the beam20.

The groove 22 may have a rectangular sectional shape, as shown in FIGS.2A, 2B, FIGS. 6A, 6B, FIG. 8, and FIGS. 12A, 12B. Alternatively, thesection of the groove 22 may have an asymmetrical shape, as shown inFIGS. 3A, 3B, FIGS. 4A, 4B, FIGS. 7A, 7B, FIGS. 10A, 10B, FIGS. 13A,13B, and FIGS. 14A, 14B. The groove 22 having any of the exemplifiedsectional shapes can provide advantageous effects such as formation of along heat conduction route.

As a function of the groove 22, there is mentioned a restriction ofmovement of heat generated on the beam 20. In addition, another functionof the groove 22 is to increase an intensity of an electric fieldapplied to the piezoelectric material of the beam 20 by using theelectrode formed in the groove 22. Furthermore, the groove 22 canmaintain mechanical strength of the beam 20 against bending, because thegroove 22 has the bottom.

The groove 22 may be a single groove or include a plurality of grooveson the beam 20. For example, as shown in FIGS. 1 to 4B, a single groove22 may be formed on a single beam 20. Alternatively, there may be formedtwo grooves 22 on the single beam 20, as shown in FIGS. 5 to 14B. Inthis case, both of the two grooves 22 may be provided on one of thesurfaces of the beam 20 perpendicular to the Z direction (See FIGS. 5 to7B), or each of the two grooves 22, respectively, may be formed on eachof the surfaces of the beam 20 perpendicular to the Z direction (SeeFIGS. 8 to FIGS. 14B).

The through-hole 24 penetrates from an inner surface of the groove 22 tothe surface of the beam 20 opposite to the surface thereof where thegroove 22 is formed. In this case, penetration of the through-hole 24from the inner surface of the groove 22 to “the surface” on an oppositeside in the beam 20 means that even when the surface on the oppositeside has an uneven portion due to a presence of an other groove or thelike formed on the opposite surface, the through-hole 24 is formed so asto reach the surface on the opposite side from the inner surface of thegroove 22. Accordingly, penetration of the through-hole 24 includespenetration to a recessed portion in the surface orthogonal to the Zaxis, and is not restricted to the penetration from the inner surface ofthe groove 22 to “the surface” on the opposite side.

The through-hole 24 may be provided as a single through-hole or aplurality of through-holes in the single groove 22. Preferably, thethrough-hole 24 may be provided in a deep position in a depth directionof the groove 22 on the inner surface of the groove 22. This can furtherfacilitate formation of the groove 22 (Details will be described later).The through-hole 24 has a round planar shape in the examples of thedrawings but this is merely an example of the planar shape thereof. Inaddition, a planar size of the through-hole 24 can be arbitrarilydetermined as long as the groove 22 can have a bottom. Now, a width ofthe through-hole 24 will be described with reference to FIGS. 2A and 2B.The through-hole 24 is formed in such a manner that a width W₂ of the Xdirection is smaller than a width W₁ in an X-axis direction of anopening portion of the groove 22. In the embodiments, the through-hole24 is formed such that the width W₂ is equal to or smaller than half ofthe width W₁. Preferably, the planar size of the through-hole 24 is madesmall to an extent not reducing the mechanical strength of the beam 20.When the plurality of through-holes 24 are provided, each of thethrough-holes 24 can be arranged in consideration of efficiency information of the groove 22. On an inner surface of the through-hole 24may be provided a conductive plug 36.

One of functions of the through-hole 24 is to increase efficiency ofetching in formation of the groove 22. In other words, forming thegroove 22 by performing wet etching on the beam 20 can prevent etchingefficiency from being reduced due to stagnation of an etchant in a deepposition of the groove 22. In that case, the etchant can be circulatedvia the through-hole 24, so that the groove 22 can be formed with anarrow width and a large depth. Such an advantageous effect becomes morenoticeable in the flexural resonator elements 100 to 400 that are morecompact in size and include the beams 20 having a narrower width. Thus,the through-hole 24 has an advantageous effect that facilitatesminiaturization of the flexural resonator elements 100 to 400.

Additionally, another function of the through-hole 24 is to control thesectional shape of the groove 22 by selecting an arrangement of thethrough-hole 24. This will be described with reference to FIGS. 3A, 3Band FIGS. 4A, 4B. As shown in the drawings, depending on the material ofthe beam 20, an etching rate of the wet etching can be anisotropic. Asthis case, for example, the beam 20 may be made of quartz crystal and aportion near the Z axis of the quartz crystal may be oriented in the Zdirection of the beam 20. In this situation, as shown in FIGS. 3A and3B, the etching rate in a specific direction becomes smaller than inother directions and thereby the sectional shape of the groove 22 maybecome close to a triangular shape. In this case, the advantageouseffect of the through-hole 24 facilitating formation of the groove 22 isexhibited. Then, furthermore, by selecting a position for forming thethrough-hole 24, the sectional shape of the groove 24 can be made closeto a rectangular shape. In other words, as shown in FIGS. 4A and 4B, thegroove 22 can have a rectangular-like sectional shape by arranging thethrough-hole 24 in consideration of anisotropy of etching in advancewhen forming the groove 22. This takes advantage of a phenomenon thatthe etching rate becomes higher in a region near the through-hole 24than in other regions due to circulation of the etchant through thethrough-hole 24. FIGS. 13A, 13B and FIGS. 14A, 14B show examples inwhich the two grooves 22 are formed to be opposed to each other. In theexamples also, the same advantageous effect can be obtained by selectingthe arrangement of the through-hole 24.

Furthermore, the through-hole 24 can also serve to prevent separation ofthe electrode formed inside the groove 24 by forming the plug 36 in thethrough-hole 24 and to allow a connection between electrodes of an uppersurface and a lower surface of the beam 20 via the through-hole 24.

The beam 20 may include at least one electrode. For example, as shown inrespective right-side sectional views of the drawings, the beam 20includes a first electrode 32 on the inner surface of the groove 22 anda second electrode 34 on a surface of the beam 20 perpendicular to the Xdirection. The first and the second electrodes 32 and 34 may be formedup onto a surface of the beam 20 perpendicular to the Z direction. Thefirst and the second electrodes 32 and 34 can be connected to anot-shown external circuit element or the like. In addition, the firstand the second electrodes 32 and 34 can serve as a driving electrodeand/or a detection electrode. For example, when an alternating currentsignal is input to the first and the second electrodes 32 and 34, at amoment in which the first electrode 32 is at higher potential than thesecond electrode 34, as shown in FIG. 15, an electric field is appliedto portions near opposite ends of the beam 20 in the X direction inmutually opposite directions and thereby the beam 20 can be bent. On theother hand, at a moment in which the first electrode 32 is at lowerpotential than the second electrode 34, the beam 20 can be bent in anopposite direction. The groove 22 allows the arrangement of theelectrodes as above, whereby a distance between the opposing electrodescan be reduced and thus the intensity of the electric field applied tothe piezoelectric material of the beam 20 can be increased. The firstand the second electrodes 32 and 34 may be structured as a laminate oflayers made of chromium (Cr) and gold (Au), for example.

The plug 36 may be formed on the inner surface of the through-hole 24.The plug 36 may have conductive properties and may be made of a metalsuch as Au, for example. As in the examples of the drawings, the plug 36may be formed so as to fill an inside of the through-hole 24.Alternatively, the plug 36 may be protruded on a surface of the beam 20not in contact with the first electrode 32 as in the examples of thedrawings.

When the groove 22 is formed only on the one of the surfaces of the beam20 perpendicular to the Z direction (FIGS. 2A to 4B, FIGS. 6A, 6B, andFIGS. 7A, 7B) and the plug 36 is formed on the inner surface of thethrough-hole 24, the first electrode 32 and the plug 36 may be connectedto each other. This structure can provide an advantageous effect thatprevents separation of the first electrode 32 from the inner surface ofthe groove 22. In this case, a portion of the plug 36 protruded on thesurface of the beam 20 not in contact with the first electrode 32 canserve as an anchor increasing the above advantageous effect.

When the groove 22 is formed on the opposite surfaces of the beam 20perpendicular to the Z direction (FIGS. 9A, 9B, FIGS. 10A, 10B, andFIGS. 12A to 14B) and the plug 36 is formed on the inner surface of thethrough-hole 24, the first electrode 32 and the plug 36 may be connectedto each other. This can prevent separation of the first electrode 32from the inner surface of the groove 22, as well as can facilitateleading of wiring of the first electrode 32. In other words, when thefirst electrodes 32 on the opposite surfaces of the beam 20 are intendedto have a same potential, wirings formed on the resonator elements canbe simplified by using the plug 36. Consequently, using the plug 36 forthe wiring can lead to reduction of problems such as wiring breaking andshort circuit.

As described above, regarding the tuning fork flexural resonatorelements 100 to 400 according to the embodiments, the beam 20 includesthe groove 22. Thus, energy loss can be reduced. In addition, since thebeam 20 also includes the through-hole 24, a compact resonator elementcan be produced easily. Furthermore, in the tuning fork flexuralresonator elements 100 to 400 according to the embodiments, formation ofthe plug 36 on the inner wall of the through-hole 24 prevents problemssuch as electrode separation, wiring breaking, and short circuit,thereby increasing reliability. Still furthermore, the tuning forkflexural resonator elements 100 to 400 can, for example, generate areference signal and thus can be applied to clocks and watches, datacommunication apparatuses, or the like.

1-2. Double T-shaped Flexural Resonator Element

FIG. 16 is a plan view exemplifying a flexural resonator element 500 asan example of the flexural resonator element according to theembodiments. In FIG. 16, the flexural resonator element 500 is anexample of a double T-shaped type.

The flexural resonator element 500 includes the base body 10 and thebeam 20 having the groove 22 and the through-hole 24 formed thereon.

The beam 20 is the same as that in the flexural resonator elements 100to 400. The groove 22 and the through-hole 24 formed on the beam 20 arealso the same as those described above. Accordingly, the flexuralresonator element 500 is the same as the flexural resonator elements 100to 400 excepting that the structure of the base body 10 and the positionand the functions of the beam 20 are different from those in theflexural resonator elements 100 to 400. Thus, descriptions of same partswill be omitted below.

The base body 10 of the flexural resonator element 500 includes a baseportion 12 and a pair of connecting portions 14. The base portion 12 isformed so as to include a position of the center of gravity of theflexural resonator element 500, so that the base portion 12 may serve tosupport the flexural resonator element 500. In the example shown in thedrawing, the base portion 12 has a rectangular planar shape, but this ismerely an example of the base portion 12.

The pair of connecting portions 14 are extended in directions oppositeto each other from the base portion 12. Specifically, the connectingportions 14 are extended in the direction (the X direction) orthogonalto the direction (the Y direction) in which the beam 20 is extended. Theconnecting portions 14 serve to support the beam 20 to be driven. Theconnecting portions 14 in the example of the drawing have a rectangularplanar shape, but may have an alternative shape.

The flexural resonator element 500 includes a pair of detection beams 26(20) extended in directions opposite to each other from the base portion12 and two pairs of driving beams 28 (20) extended in directionsopposite to each other from the connecting portions 14. The beams 20included in the flexural resonator element 500 are all extended in the Ydirection and flexurally vibrate in the X direction. Naming of thedouble T-shape stems from a type in which the driving beams 28 (20)protruded from the connecting portions 14 form an alphabetical T-likeshape and such two T-like shapes are connected to each other. However,the shape of the flexural resonator element 500 of the embodiment is notspecifically restricted by the name of the double T-shaped type.

Similarly to the flexural resonator elements 100 to 400, the flexuralresonator element 500 described above includes the beams 20 with thegroove 22 formed thereon, thereby reducing energy loss. In addition,since the through-hole 24 is formed in each of the beams 20, theflexural resonator element 500 having a compact size can be producedeasily. Furthermore, in the flexural resonator element 500, forming theplug 36 on the inner wall of the through-hole 24 can prevent problemssuch as electrode separation, wiring breaking, and short circuit,thereby increasing reliability. The flexural resonator element 500 candetect, for example, acceleration and angular acceleration and thus canbe applied to digital cameras, motor vehicles, or the like.

1-3. Double-Ended Tuning Fork Resonator Element

FIG. 17 is a plan view exemplifying a flexural resonator element 600 asan example of the flexural resonator element according to theembodiments. In FIG. 17, the flexural resonator element 600 is anexample of a double-ended tuning fork resonator element.

The flexural resonator element 600 includes two base bodies 10. The basebodies 10 in the flexural resonator element 600 are substantially thesame as the base body 10 in the flexural resonator elements 100 to 400.As indicated by broken lines in FIG. 17, the base bodies 10 of theflexural resonator element 600 may form a frame-shaped (a pictureframe-shaped) portion 16 having an opening portion 18 formed within theframe-shaped portion 16. In the example of the drawing, the frame-shapedportion 16 has a rectangular shape, but this is merely an example of theshape thereof. In formation of the frame-shaped portion 16, the two basebodies 10 are integrated with each other by the frame-shaped portion 16.In this case, there may be formed two beams 620 in such a manner thatopposite ends of the beams 620 are supported by the frame-shaped portion16 of the base bodies 10 and the two beams 620 are bridged in parallelto each other in the opening portion 18. The frame-shaped portion 16 maybe made of a same material as that of the base bodies 10. When the basebodies 10 include the frame-shaped portion 16, strength of the flexuralresonator element 600 can be increased, thus facilitating handling orthe like of the flexural resonator element 600.

The flexural resonator element 600 includes the two beams 620 formed inparallel to each other. The opposite ends of each of the beams 620 aresupported by the base bodies 10. In the example of the drawing, the eachbeam 620 has four grooves 622 formed thereon. Each two of the fourgrooves 622, respectively, are formed on each of two surfaces of thebeam 620 perpendicular to the Z direction.

The two beams 620 of the flexural resonator element 600 can beconsidered to be equivalent to the two beams 20 connected opposed toeach other in the flexural resonator elements 100 to 400. An extendingdirection and a vibrating direction of each of the beams 620 aresubstantially the same as those of the beam 20.

Each of the beams 620 is extended from the base bodies 10 in the Ydirection and flexurally vibrates in the X direction. In addition, theeach beam 620 includes the grooves 622 and a through-hole 624.

As shown in FIG. 17, in the flexural resonator element 600, each beam620 has the four grooves 622, each two of which are formed on adifferent one of the two surfaces of the beam 620 perpendicular to the Zdirection. A sum of planar sizes of the four grooves 622 may be in arange of 10 to 80% of a length of the beam 620, for example. Preferably,the grooves 622 are formed so as to be closer to portions of the beam620 connecting with the base bodies 10. This allows the grooves 622 tobe positioned in a region exhibiting a large amount of deformation whenthe beam 620 is bent, so that a mass can be left near a center of thebeam 620. Additionally, in association with leading of the electrode orthe like, and when performing frequency adjustment of the flexuralresonator element 600 by adhering a weight material to a top end of thebeam 620, it is unnecessary to form the grooves 622 over an entirelength of the beam 620.

A sectional shape and functions of the grooves 622 are substantially thesame as those of the groove 20 included in the flexural resonatorelements 100 to 400.

The through-hole 624 penetrates from an inner surface of the groove 622to a surface of the beam 620 opposite to the surface thereof where thegroove 622 is formed. Functions, mechanism, and advantageous effects ofthe through-hole 624 are the same as those of the through-hole 24 of thebeam 20 in the flexural resonator elements 100 to 400, and thusdescriptions of those parts will be omitted herein.

Similarly to the flexural resonator elements 100 to 400, in the flexuralresonator element 600 described above, the beam 620 has the grooves 622formed thereon to reduce energy loss. In addition, the beam 620 also hasthe through-hole 624 formed therein, thereby facilitating production ofa compact flexural resonator element. Furthermore, in the flexuralresonator element 600, forming a plug on an inner wall of thethrough-hole 624 can prevent problems such as electrode separation,wiring breaking, and short circuit, thereby increasing reliability. Forexample, the flexural resonator element 600 can detect stress in the Ydirection, thus being applicable to pressure sensors or the like.

2-1. Method for Producing Flexural Resonator Element

The flexural resonator element according to the embodiments may beproduced by a following method, for example. FIGS. 18 to 27 aresectional views schematically showing steps for producing the flexuralresonator element according to the embodiments. The following productionmethod is merely an example.

As shown in FIG. 18, first, there is prepared a Z plate of quartzcrystal, as a substrate 1. The Z plate of quartz crystal may be cut outfrom a single crystal of quartz crystal by inclining an XY plane formedby an X axis and a Y axis at an angle of approximately 1 to 5 degreesaround the X axis in a counterclockwise direction in an orthogonalcoordinate system having the X, Y, and Z-axes.

Next, on each of upper and lower surfaces of the substrate 1 is formed ametal film 2 structured as a laminate of layers of Cr and Au, by anot-shown sputtering apparatus. Then, photolithography is used toperform patterning of a resist layer 3 or the like on the metal film 2thus formed (See FIG. 18). The patterning has an outline shape of theflexural resonator element to be produced.

Next, as shown in FIG. 19, an outline of the flexural resonator elementshown in the respective plan views above is formed by the patterning ofthe metal film 2. In this case, for example, etching using a hydrogenfluoride solution may be performed on the substrate 1. FIG. 19 shows asection of the beam 20 or the beam 620 in that situation.

Hereinafter, a description will be given separately of when thethrough-hole connects the inner surface of the groove to the surface ofthe beam opposite to the inner surface and when the through-holeconnects the inner surface of the groove to an inner surface of anothergroove formed on the opposite surface of the beam.

In the case of the through-hole connecting the inner surface of thegroove to the opposite surface of the beam, as shown in FIG. 20, thepatterning is made on the metal film 2 in accordance with the shapes ofthe groove and the through-hole. The patterning may be performed byforming a patterned resist mask on the metal film 2 in advance. In thepatterning, a pattern of the groove 22 (622) is formed on the surfacewhere the groove 22 (622) of the beam 20 (620) is to be formed, and apattern of the through-hole 24 (624) is formed on the opposite surface(See FIG. 22).

Then, as shown in FIGS. 21 and 22, the groove 22 (622) and thethrough-hole 24 (624) are formed by etching. The etching may be wetetching using hydrogen fluoride or the like. Wet etching achieves largeetching rate, so that etching time can be reduced. FIG. 21 shows asituation during the etching in the step. As shown in FIG. 21, theetching of the step allows an etched top end of the groove to meet anetched top end of the through-hole at some point of the beam. In thisexample, the etching of the groove and the etching of the through-holeare simultaneously performed. However, a hole to be used as thethrough-hole 24 (624) may be formed before the etching of the groove. Inthis manner, as shown in FIG. 22, the flexural resonator element can beproduced in such the manner that the through-hole connects the innersurface of the groove to the opposite surface of the beam.

On the other hand, when the through-hole connects the inner surface ofthe groove to the inner surface of the other groove formed on theopposite surface of the beam, the outline of the flexural resonatorelement is formed as in FIG. 19, and then, patterning is performed onthe metal film 2 formed on one of surfaces of the beam 20 (620)orthogonal to the Z direction, as shown in FIG. 23. The patterningcorresponds to a position for forming the through-hole 24 (624). Thepatterning may be performed by forming a patterned resist mask on themetal film 2 in advance.

Next, as shown in FIG. 24, using the metal film 2 as a mask, the hole tobe used as the through-hole 24 (624) is formed. The formed hole may havea depth ranging, for example, from 5 to 95% of a thickness of the beam20 (620) in the Z direction. The step can be performed by dry etching orwet etching. When the step uses dry etching, the hole can be made moreisotropic due to a small anisotropy in etching rate. As an example ofdry etching, plasma etching may be used.

Next, as shown in FIG. 25, in order to form the groove 22 (622),patterning is further performed on the metal film 2. Then, as shown inFIGS. 26 and 27, the groove 22 (622) is etched. The etching may be wetetching using hydrogen fluoride or the like. Wet etching exhibits highetching rate, so that etching time can be reduced. FIG. 26 shows asituation during the etching in the step. At the step, the hole as thethrough-hole 24 (624) previously formed can be simultaneously etched ina manner maintaining a shape of the hole. Accordingly, the etching ofthe step, as shown in FIG. 26, allows the etched top end of the grooveto meet an etched top of the hole as the through-hole at some point ofthe beam. Then, finally, as shown in FIG. 27, the flexural resonatorelement can be produced in such the manner that the through-holeconnects the inner surface of the groove to the inner surface of theother groove formed on the opposite surface of the beam.

In the example described above, the depth of the hole as thethrough-hole 24 (624) can be designed in such the manner that the holeis connected to the deep position of the groove 22 (622) where etchantstagnation occurs upon etching of the groove 22 (622). This can optimize(minimize) a sum of a time for forming the hole as the through-hole 24(624) and a time for forming the groove 22 (622).

As described above, the method of the embodiment can produce theflexural resonator element according to the embodiments. The productionmethod according to the embodiment may further include forming anelectrode if necessary. For example, there may be formed an electrode byproviding a metal layer on an entire surface of the flexural resonatorelement by sputtering or the like and then patterning the metal layer.

The flexural resonator element production method of the embodimentincludes following characteristics. At the step of forming the groove 22(622) by wet etching of the beam 20 (620), the production method canprevent etching efficiency reduction due to stagnation of the etchant inthe deep position of the groove 22 (622). In other words, the etchantcan be circulated via the through-hole 24 (624) connected to the deepposition of the groove 22 (622), so that the groove 22 (622) can be madenarrow and deep. Therefore, the production method of the embodimentenables the narrow and deep groove to be easily formed on the beam,thereby facilitating production of a compact flexural resonator element.

3. Flexural Resonator

FIG. 28 is a sectional view schematically showing a flexural resonator1000 according to an embodiment of the invention. The flexural resonator1000 of the embodiment includes any one of the above-described flexuralresonator elements, a casing 700, and a cover 800. In the example of thedrawing, the flexural resonator 1000 includes the flexural resonatorelement 100.

The casing 700 has a container-like shape where the flexural resonatorelement 100 can be stored. A planar shape of the casing 700 is notspecifically restricted. An upper part of the casing 700 has an openingenough to place the flexural resonator element 100 in the casing 700.The opening of the casing 700 can be airtightly sealed with the cover800. Inside and outside the casing 700, there may be provided a wiringpattern 50 for external connection, as shown in the drawing. Inaddition, the casing 700 may include a through-hole 60, as in thedrawing, so as to establish an electrical connection between an insideand an outside of the casing 700 via the through-hole 60. The casing 700may be made of an inorganic material such as ceramic or glass.

The cover 800 has a flat plate-like shape to seal the opening of theupper part of the casing 700. The cover 800 has an arbitrary planarshape as long as the cover can seal the opening of the casing 700. Thecover 800 is made of ceramic, glass, a metal, or the like. For example,the casing 700 may be adhered to the cover 800 by plasma welding, seamwelding, ultrasonic bonding, an adhesive agent, or the like. A cavity 70formed by the casing 700 and the cover 800 is a space where the flexuralresonator element is driven. The cavity 70 can be sealed off, wherebythe flexural resonator element can be placed in a pressure-reduced spaceor an inert-gas atmosphere.

The flexural resonator element is provided in the cavity 70 formed bythe casing 700 and the cover 800. For example, the flexural resonatorelement may be fixed on an inner wall surface of the cavity 70 (a bottomsurface of the casing 700 in the example of the drawing) by an adhesiveagent, paste, wax, or the like. The flexural resonator element of theexample of the drawing is fixed on the bottom surface of the casing 700by an adhesive layer 80, and a base body 100 is fixed to the flexuralresonator element to cantilever-support the resonator element.

The flexural resonator 1000 thus formed includes the flexural resonatorelement according to any one of the embodiments. Accordingly, theflexural resonator 1000 can reduce energy loss and can be easilyproduced as a compact flexural resonator. In addition, the flexuralresonator 1000 including the flexural resonator element of any one ofthe embodiments has high reliability, and thus, can be applied toproducts in a variety of fields.

Embodiments of the invention are not restricted to the embodimentsdescribed above, and various modifications and changes can be made. Forexample, there may be embodiments of the invention that includesubstantially the same structures as those described in the embodiments(for example, functions, methods, and results may be the same as thosein the embodiments, or advantages and advantageous effects may be thesame as those in the embodiments). Additionally, an other embodiment ofthe invention may include a structure whose non-essential parts aredifferent from those of the structures in the embodiments. Furthermore,there may be an embodiment including a structure that can provide thesame advantageous effects as those described in the embodiments or astructure that can achieve the same advantages of the embodiments, aswell as an embodiment including a known technique added to the structuredescribed in the embodiments.

The flexural resonator element according to the embodiments reducesenergy loss, has high reliability, and can be easily miniaturized.Accordingly, mounting the flexural resonator element of the embodimentsin products of various fields allows production of more compact productsachieving higher performance.

The entire disclosure of Japanese Patent Application No. 2009-034861,filed Feb. 18, 2009 is expressly incorporated by reference herein.

1. A flexural resonator element, comprising: a base body; and a beamwith two grooves and a through-hole, the beam being extended in a Ydirection from the base body and flexurally vibrating in an X directionorthogonal to the Y direction, the two grooves being formed on a surfaceof the beam perpendicular to a Z direction orthogonal to the X directionand the Y direction, and the through-hole having a smaller width in theX direction than a width of an opening of the groove in the X directionand penetrating from an inner surface of the groove formed on thesurface of the beam to a surface of the beam opposite to the surface ofthe beam having the groove.
 2. The flexural resonator element accordingto claim 1, wherein the through-hole includes a plurality ofthrough-holes, the plurality of through-holes being formed in thegroove.
 3. The flexural resonator element according to claim 1, whereinthe beam includes a first electrode provided on the inner surface of thegroove, a second electrode provided on a surface of the beamperpendicular to the X direction, and a plug provided on an innersurface of the through-hole.
 4. The flexural resonator element accordingto claim 1, wherein the base body and the beam are made of quartzcrystal.
 5. The flexural resonator element according to claim 1, whereinthe flexural resonator element is of a tuning fork type in which thebeam includes two cantilevered beams extended in parallel to each otherfrom the base body.
 6. The flexural resonator element according to claim1, wherein the base body includes a base portion and a pair ofconnecting portions extended from the base portion in directionsopposite to each other, and the beam includes a pair of detection beamsextended from the base portion in directions opposite to each other andtwo pairs of driving beams extended from the connecting portion indirections opposite to each other.
 7. A flexural resonator, comprising:the flexural resonator element of claim 1; a casing housing the flexuralresonator element; and a cover sealing the casing.